1. Field of the Invention
The present invention relates generally to a rigid mooring system for use in attaching a floating vessel or ship to a tower structure attached to the sea floor. More particularly, the invention relates to a tower mooring system comprising a rigid tower yoke assembly having a yoke releasably attached to a yoke head via a connector allowing removal of the yoke by the ship in the event of predicted abnormally high sea states.
2. Description of the Related Art
Typical tower yoke mooring systems are permanent mooring systems where the floating vessel cannot leave for a storm. The typical tower yoke, single point mooring system includes a “soft yoke” for mooring a floating vessel directly to a fixed tower. A turntable is fastened to the tower, typically with a roller bearing, to allow the floating vessel to freely weathervane about the fixed tower. A yoke is connected to the turntable with pitch and roll joints to allow the vessel to pitch and roll. The yoke includes a large ballast tank adapted to be filled with water to provide the necessary restoring force to minimize vessel motions. Two mooring links suspend the ballast tank from a support structure mounted on the floating vessel.
Product, such as oil or gas for example, is transferred from the tower across swivels located on the turntable and through hoses from the turntable to the vessel. The tower includes deck space for a manifold and other equipment. Access to the tower can be made via walkways from the vessel and on the yoke.
However, some tower yoke mooring system applications in shallow water are needed in areas potentially subjected to large storms or extreme sea states such as hurricanes or typhoons, during which the floating vessel will leave the area. For purposes of safety and to survive the extreme sea states it is desirable that the tower yoke be disconnectable from the tower structure.